“Dead bodies, at least 100, scattered around the encounter area,” he said.

Lieutenant Colonel Jo-Ar Herrera said his security forces were edging towards the business area of Marawi City, which is under the control of the combatants who have sworn allegiance to Isis.

There are around 200 Islamist fighters who have taken up sniper positions, he said. “The battlefield is very fluid.”

US troops are located close to Marawi City but are not actively fighting Isis insurgents, a Philippines military spokesman said.

“There are some US personnel who are operating equipment to provide information on situation awareness to our troops,” Brigadier General Restituto Padilla told a news conference. “I do not know the exact number and the specific mission. They are allowed to carry rifles for self-defence. But they are not allowed to fight, they only provide support.”

President Rodrigo Duterte placed the entire Mindanao region under martial law after the Maute, a radical Islamic organisation, backed by other jihadist extremists, attacked Marawi City.